ius gentium or a separate peace

On this day in 1928, the France and US sponsored Kellogg-Briand Pact—officially the General Treaty for Renunciation of War as an Instrument of National Policy—was signed in Paris by representatives of Australia, Belgium, Canada, Czechoslovakia, Germany, British India, the Irish Free State, the UK, New Zealand, Poland and South Africa to go into effect the following summer.
Named for the authors and chief negotiators US Secretary of State Frank B Kellogg and French Foreign Minister Aristide Briand, as the treaty was framed and acceded to outside of the League of Nations, the treaty remains in effect with Barbados ratifying it (along with most other countries) as late as 1971. Though failing rather spectacularly to prevent World War II (thirty one states had signed on by the 1929 effective date, including Austria, the Kingdom of the Serbs, Croats and Slovenes, Spain, Switzerland, Japan, Italy, China and the Soviet Union), aggressions and occupations continued apace but without any formal declarations by the treaties signatories, it did subsequently encourage diplomacy through its requirement to establish conciliation commissions (normalising sanctions and tariffs as weapons preferable to military force) for conflict resolution and provided the framework to prosecute war-crimes, conceived as crimes against peace.